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1.
SmAlO3 nanopowder synthesized by a citrate precursor method using citric acid as a chelating agent and ethylene glycol as an esterifying
agent was reported in this paper. The phase purity of the as-prepared powder was examined using thermogravimetry (TG) analysis
and differential scanning calorimetry (DSC) analysis, Fourier transform infrared spectroscopy (FTIR). The X-ray diffraction
(XRD) studies showed that pure SmAlO3 phase with orthorhombic perovskite structure could be synthesized at 800 °C for 2 h without any detectable intermediate phase.
The average particle size calculated from transmission electron microscopy (TEM) investigation for the powder synthesized
at 900 °C was as low as 45 nm. The nanopowder was sintered to a density of 97% of the theoretical density at 1,550 °C for
2 h and the bulk ceramics exhibited excellent microwave dielectric properties as follows: a dielectric constant of 20.54,
a quality factor of 75,380 GHz and a temperature coefficient of resonate frequency of −69.2 ppm/K. 相似文献
2.
Akira Inaba Hal Suzuki Jan Krawczyk Maria Massalska-Arod
《Chemical physics letters》2008,463(1-3):90-93
The heat capacity of two glass formers 5*CB and 8*OCB, each of which has two crystalline polymorphs (phases I and II) as well as a glass phase, was determined between 0.35 K and 20 K. The T-linear term of the heat capacity becomes significant below 1 K for both glasses. The glassy crystalline phase II of 5*CB also shows such contribution, which is consistent with the existence of a residual entropy. Unexpectedly, however, the ‘stable’ phase II of 8*OCB shows the similar contribution, indicating that this phase is disordered, whereas the glassy crystalline phase I shows no such contribution. 相似文献
3.
Boldyreva E. V. Shakhtshneider T. P. Ahsbahs H. Sowa H. Uchtmann H. 《Journal of Thermal Analysis and Calorimetry》2002,68(2):437-452
Effect of hydrostatic pressure on the two (I – monoclinic and II – orthorhombic) polymorphs of paracetamol was studied by
X-ray diffraction in the diamond anvil cell at pressures up to 4.5 GPa (for the monoclinic form) and up to 5.5 GPa (for the
orthorhombic form). The two groups of phenomena were studied: (i) the anisotropic structural distortion of the same polymorph,
(ii) transitions between the polymorphs induced by pressure.
The anisotropy of structural distortion of polymorphs I and II was well reproducible from sample to sample, also from powder
samples to single crystals. The bulk compressibility of the two forms was shown to be practically the same. However, a noticeable
qualitative difference in the anisotropy of structural distortion was observed: with increasing pressure the structure of
polymorph II contracted in all the directions showing isotropic compression in the planes of hydrogen-bonded molecular layers,
whereas the layers in the structure of the polymorph I expanded in some directions. Maximum compression in both polymorphs
I and II was observed in the directions normal to the molecular layers.
The transitions between the polymorphs induced by pressure were poorly reproducible and depended strongly on the sample and
on the procedure of increasing/decreasing pressure. No phase transitions were induced in the single crystals of the monoclinic
polymorph at pressures at least up to 4GPa, although a partial transformation of polymorph I into polymorph II was observed
at increased pressure in powder samples. Polymorph II transformed partly into the polymorph I during grinding. The transformation
could be hindered if grinding was carried out in CCl4.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
The thermal behaviour of nifedipine was studied with the view to understand the various phase transitions between its polymorphs. The focus was on polymorph identification, accompanying morphological changes during crystallization and the nature of the phase transformations. These features were compared to the complexity of the crystallization mechanisms, studied by dynamic differential scanning calorimetry (DSC) heating techniques. DSC, thermogravimetry (TG) established the temperature limits for preparation of amorphous nifedipine from the melt. DSC studies identified that metastable form B, melting point ∼163 °C, was enantiotropically related to a third modification, form C, which existed at lower temperatures. Form C converted endothermically to form B at ∼56 °C on heating and was shown by hot stage microscopy (HSM) to be accompanied by morphological changes. Modulated temperature differential scanning calorimetry (MTDSC) showed discontinuities in the reversing heat flow signal during crystallization of amorphous nifedipine (from ∼92 °C) to form B, which suggested that a number of polymorphs may nucleate from the melt prior to form B formation. Identification of the number of nifedipine polymorphs included the use of combined DSC-powder X-ray diffraction (PXRD) and variable temperature powder X-ray diffraction (VTPXRD). The crystallization kinetics studied by dynamic DSC heating techniques followed by analysis using the Friedman isoconversion method where values of activation energy (E) and frequency factor (A) were estimated as a function of alpha or extent of conversion (α). The variations in E with α, from 0.05 to 0.9, for the amorphous to form B conversion could indicate the formation of intermediate polymorphs prior to form B. The form B to form A conversion showed a constancy in E on kinetic analysis from α 0.05 to 0.9, which suggested that a constant crystallization mechanism operated during formation of the thermodynamically stable form A. 相似文献
5.
Mary C. F. Alves Soraia C. Souza Márcia R. S. Silva Elaine C. Paris S. J. G. Lima R. M. Gomes E. Longo A. G. de Souza Iêda M. Garcia dos Santos 《Journal of Thermal Analysis and Calorimetry》2009,97(1):179-183
SrSnO3 was synthesized by the polymeric precursor method with elimination of carbon in oxygen atmosphere at 250 °C for 24 h. The
powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After calcination at 500, 600
and 700 °C for 2 h, samples were evaluated by X-ray diffraction (XRD), infrared spectroscopy (IR) and Rietveld refinement
of the XRD patterns for samples calcined at 900, 1,000 and 1,100 °C. During thermal treatment of the powder precursor ester
combustion was followed by carbonate decomposition and perovskite crystallization. No phase transition was observed as usually
presented in literature for SrSnO3 that had only a rearrangement of SnO6 polyhedra. 相似文献
6.
以不同方法制备了两种不同晶型的酞菁氧钒(VOPc),X-射线分析结果表明,一为多晶型,另一种为非晶型。两种晶型在红外区都具有光导性,非晶型的光导性更好。 相似文献
7.
Nano-sized La1/2Nd1/2FeO3 (LNF) powder is synthesized by the sol–gel citrate method. The Rietveld refinement of the X-ray diffraction profile of the sample at room temperature (303 K) shows the orthorhombic phase with Pbnm symmetry. The particle size is obtained by transmission electron microscope. The antiferromagnetic nature of the sample is explained using zero field cooled and field cooled magnetisation and the corresponding hysteresis loop. A signature of weak ferromagnetic phase is observed in LNF at low temperature which is explained on the basis of spin glass like behaviour of surface spins. The dielectric relaxation of the sample has been investigated using impedance spectroscopy in the frequency range from 42 Hz to 1 MHz and in the temperature range from 303 K to 513 K. The Cole–Cole model is used to analyse the dielectric relaxation of LNF. The frequency dependent conductivity spectra follow the power law. The magneto capacitance measurement of the sample confirms its multiferroic behaviour. 相似文献
8.
Micro-Raman spectroscopy is a powerful technique for qualitative and quantitative analysis of different mineral mixtures. In this paper, micro-Raman spectroscopy was used for quantification in local regions (180 × 180 μm area) of ternary mixtures of the synthetic calcium carbonate (CaCO3) polymorphs (vaterite, aragonite, calcite) as well as CaCO3 formed during the carbonation of nanolime suspension. The obtained results of localized quantification were in agreement with the detected concentrations obtained from bulk quantitative phase analysis of X-ray powder diffraction patterns. The detection limits were found to be below 0.5 wt.% for each CaCO3 polymorphs. Through the use of 2D mapping, localized quantification of CaCO3 polymorphs can be achieved. This information could be potentially useful for conservation of valuable Cultural Heritage objects, as it might influence the consolidation treatment chosen. 相似文献
9.
Chun-Hong Jiang Li-Fang Song Cheng-Li Jiao Jian Zhang Li-Xian Sun Fen Xu Yong Du Zhong Cao 《Journal of Thermal Analysis and Calorimetry》2011,103(1):373-380
A three-dimensional lithium-based metal–organic framework Li2(2,6-NDC) (2,6-NDC = 2,6-naphthalene dicarboxylate) has been synthesized solvothermally and characterized by X-ray powder
diffraction, elemental analysis, FT-IR spectroscopy, thermogravimetry and mass spectrometer analysis (TG–MS). The framework
has exceptional stability and is stable to 863 K. The thermal decomposition characteristic of this compound was investigated
through the TG–MS from 293 to 1250 K. The molar heat capacity of the compound was measured by temperature modulated differential
scanning calorimetry (TMDSC) over the temperature range from 195 to 670 K for the first time. The thermodynamic parameters
such as entropy and enthalpy versus 298.15 K based on the above molar heat capacity were calculated. 相似文献
10.
Polymorphism and structural mechanism of the phase transformation of phenyl carbamate (PC) 总被引:1,自引:0,他引:1
Crystallization experiments with phenyl carbamate as a hydrogen-bond donor with crown ethers have led to the discovery of three unknown polymorphs of phenyl carbamate. In this contribution, we characterize the phenyl carbamate polymorphs by a variety of methods including variable temperature powder X-ray diffraction (PXRD), vibrational spectroscopy (infrared and Raman), calorimetry (DSC) and optical microscopy (HSM). The phase transformation from form I to form II is rapid by both solution-mediated and solid state transformation processes. Through comparison of the two structures of form I and form II it is possible to propose a mechanism for the transformation. 相似文献
11.
《Journal of solid state chemistry》2004,177(4-5):1667-1671
The crystal structures of BaTbO3 have been investigated over a wide temperature range between 40 and 773 K using high-resolution time-of-flight neutron powder diffraction. Two-phase transitions were observed. Below about 280 K, BaTbO3 adopts an orthorhombic perovskite structure (space group Ibmm), which is characterized by rotation of TbO6 octahedra about the pseudocubic two-fold axis. Above 280 K, BaTbO3 undergoes a first-order phase transition to a tetragonal symmetry (space group I4/mcm), in which the tilting of the octahedra is around the pseudocubic four-fold axis. As the temperature is further increased, BaTbO3 adopts the primitive cubic aristotype at about 623 K. This later phase transformation is characterized by a gradual decrease of the rotation angle, indicating a continuous phase transition, which is described by a critical exponent β=0.35. 相似文献
12.
Journal of Thermal Analysis and Calorimetry - The cell parameters of synthetic pyrope were measured in the temperature range 100–630 K by the X-ray powder diffraction method.... 相似文献
13.
Concepción Foces-Foces María Victoria Roux Rafael Notario Marta Segura 《Journal of Thermal Analysis and Calorimetry》2011,105(3):747-756
A thermophysical study of the sulfur containing amino acids l-cysteine and l-cystine has been carried out by differential scanning calorimetry (DSC). Heat capacities of both compounds were measured
in the temperature interval from T = 268 K to near their respective melting temperatures. DSC and variable temperature powder X-ray diffraction analysis (PXRD)
gave evidence for a solid–solid phase transition close to the melting point only in the l-cysteine sample. DSC experiments show that this solid–solid transition is not reversible in the temperature interval T = 235–485 K and presents a behavior depending on heating temperature, time, and rate. This behavior is also supported by
variable-temperature PXRD. The patterns for the commercial samples, at room temperature, are consistent with those simulated
for the orthorhombic and hexagonal polymorphic forms from the single-crystal X-ray analysis. 相似文献
14.
Boldyreva Elena V Drebushchak V. A. Paukov I. E. Kovalevskaya Yulia A. Drebushchak Tatiana N 《Journal of Thermal Analysis and Calorimetry》2004,77(2):607-623
Monoclinic (I) and orthorhombic (II) polymorphs of paracetamol were studied by DSC and adiabatic calorimetry in the temperature
range 5 - 450 K. At all the stages of the study, the samples (single crystals and powders) were characterized using X-ray
diffraction. A single crystal → polycrystal II→ I transformation was observed on heating polymorph II, after which polymorph
I melted at 442 K. The previously reported fact that the two polymorphs melt at different temperatures could not be confirmed.
The temperature of the II→I transformation varied from crystal to crystal. On cooling the crystals of paracetamol II from
ambient temperature to 5 K, a II→ I transformation was also observed, if the 'cooling-heating' cycles were repeated several
times. Inclusions of solvent (water) into the starting crystals were shown to be important for this transformation. The values
of the low-temperature heat-capacity of the I and II polymorphs of paracetamol were compared, and the thermodynamic functions
calculated for the two polymorphs.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
Šalitroš I Fuhr O Eichhöfer A Kruk R Pavlik J Dlháň L Boča R Ruben M 《Dalton transactions (Cambridge, England : 2003)》2012,41(17):5163-5171
The mononuclear compound (1) [Fe(II)(L)(2)](BF(4))(2) (L = 4-ethynyl-2,6-bis(pyrazol-1-yl)pyridine) was prepared and structurally as well as magnetically characterised. The crystallisation revealed the formation of two polymorphs--the orthorhombic 1A and the tetragonal form 1B. A third, intermediate phase 1C was found exhibiting a different orthorhombic space group. Reversibility of the phase transition between 1A and 1C was studied by variable-temperature single-crystal and powder X-ray diffraction studies, while an irreversible phase transition was observed for the transition of 1B→1C. The magnetic studies show that the 1A?1C transition is accompanied by a very abrupt spin transition (ST) with 8 K hysteresis width (T(1/2)(↓) = 337 K, T(1/2)(↑) = 345 K). The ST was confirmed by M?ssbauer spectroscopy as well as by DSC studies. In contrast, the 1B polymorph remained low-spin up to 420 K. In conclusion, a full cycle of intertwined phase- and spin-conversions of three polymorphs could be proven following the general scheme 1B→1C?1A. 相似文献
16.
NV Surovtsev SV Adichtchev VK Malinovsky AG Ogienko VA Drebushchak AY Manakov AI Ancharov AS Yunoshev EV Boldyreva 《The Journal of chemical physics》2012,137(6):065103
Glycine phases formed when aqueous solutions were frozen and subsequently heated under different conditions were studied by Raman scattering, x-ray diffraction, and differential scanning calorimetry (DSC) techniques. Crystallization of ice I(h) was observed in all the cases. On cooling at the rates of 0.5 K∕min and 5 K∕min, glassy glycine was formed as an intermediate phase which lived about 1 min or less only, and then transformed into β-polymorph of glycine. Quench cooling of glycine solutions (15% w∕w) in liquid nitrogen resulted in the formation of a mixture of crystalline water ice I(h) and a glassy glycine, which could be preserved at cryogenic temperatures (80 K) for an indefinitely long time. This mixture remained also quite stable for some time after heating above the cryogenic temperature. Subsequent heating under various conditions resulted in the transformation of the glycine glass into an unknown crystalline phase (glycine "X-phase") at 209-216 K, which at 218-226 K transformed into β-polymorph of glycine. The "X-phase" was characterized by Raman spectroscopy; it could be obtained in noticeable amounts using a special preparation technique and tentatively characterized by x-ray powder diffraction (P2, a = 6.648 A?, b = 25.867 A?, c = 5.610 A?, β = 113.12[ordinal indicator, masculine]); the formation of "X-phase" from the glycine glassy phase and its transformation into β-polymorph were followed by DSC. Raman scattering technique with its power for unambiguous identification of the crystalline and glassy polymorphs without limitation on the crystallite size helped us to follow the phase transformations during quenching, heating, and annealing. The experimental findings are considered in relation to the problem of control of glycine polymorphism on crystallization. 相似文献
17.
The crystal structure of the “zero-strain” positive electrode material Li4Ti5O12 was characterized by neutron powder diffraction in the temperature range 3.4 K–300 K. No phase transition was detected, and the thermal evolution of lattice parameters has been evaluated by the 2nd order Grüneisen approximation using the Debye formalism for internal energy and intrinsic anharmonicity contributions. A relatively high Debye temperature θD = 689 ± 71 K was determined. The thermal behavior of cation-anion bond lengths in octahedral and tetrahedral environments is discussed. The lithium diffusion pathway in Li4Ti5O12 was discussed on the basis of bond-valence modeling. 相似文献
18.
G. Panneerselvam R. Venkata Krishnan K. Nagarajan M. P. Antony 《Journal of Thermal Analysis and Calorimetry》2010,101(1):169-173
Dysprosium hafnate is a candidate material for as control rods in nuclear reactor because dysprosium (Dy) and hafnium (Hf)
have very high absorption cross-sections for neutrons. Dysprosium hafnate (Dy2O3·2HfO2-fluorite phase solid solution) was prepared by solid-state as well as wet chemical routes. The fluorite phase of the compound
was characterized by using X-ray diffraction (XRD). Thermal expansion characteristics were studied using high temperature
X-ray diffraction (HTXRD) in the temperature range 298–1973 K. Heat capacity measurements of dysprosium hafnate were carried
out using differential scanning calorimetry (DSC) in the temperature range 298–800 K. The room temperature lattice parameter
and the coefficient of thermal expansion are 0.5194 nm and 7.69 × 10−6 K−1, respectively. The heat capacity value at 298 K is 232 J mol−1 K−1. 相似文献
19.
HgI2 crystallizes under ambient conditions from various solvents and by sublimation into three concomitant polymorphs whose colors are red, orange, and yellow. The orange and yellow phases are metastable and transform into the red phase when touched. A phase transition from red to yellow occurs at 400 K. The reverse transition from yellow to red shows a huge hysteresis. We established that the structures of the metastable yellowM phase (determined by single‐crystal X‐ray diffraction) and the high‐temperature yellowHT phase (determined by powder synchrotron X‐ray diffraction and second‐harmonic generation) are different, albeit closely related. Both show analogous packings of I? Hg? I molecules, which are straight in the first and bent with an angle of ca. 160° in the second. The red and orange phases are tetrahedral semiconductor structures that sublime even at room temperature. The growth of the yellowM phase from 2‐chloroethanol and the kinetics of the reconstructive phase transition red to yellowHT and back were studied by optical microscopy, Raman spectroscopy in solution, luminescence, and powder synchrotron X‐ray diffraction as a function of time at various temperatures. Both yellow phases grow by accretion of HgI2 molecules, present in the solution or liberated from the red crystals, on the surface of the crystal. In contrast, the reverse transformation from yellow to red occurs in the bulk of the crystal, presumably by migration of Hg in the packing of I and subsequent rearrangement of I. The displacement parameters of Hg in both structures are considerably larger than those of I and apparently not dominated by disorder effects. 相似文献
20.
Edward Krzyżak Alina Wojakowska Andrzej Wojakowski Marek Wołcyrz 《Journal of Thermal Analysis and Calorimetry》2010,101(2):541-547
Phase diagram for the system CuBr–LiBr was determined by differential scanning calorimetry and X-ray powder diffraction. The
system exhibits a significant solid solubility of the components, especially LiBr in the respective polymorphic modifications
of CuBr. Another feature of the system CuBr–LiBr is the occurrence of five invariant three-phase equilibria, which have been
assigned to one eutectic (684 K), one peritectoid (668 K), and three eutectoids (679, 645, and 521 K). From the experimental
results, formation of a compound LiCuBr2, at 521 K is discerned. 相似文献